Jon Ostrower, writing at The Air Current (Ostrower has been reporting on — and cultivating sources in — the aviation industry for decades):

Every airplane development is a series of compromises, but to
deliver the 737 Max with its promised fuel efficiency, Boeing had
to fit 12 gallons into a 10 gallon jug. Its bigger engines made
for creative solutions as it found a way to mount the larger CFM
International turbines under the notoriously low-slung jetliner.
It lengthened the nose landing gear by eight inches, cleaned up
the aerodynamics of the tail cone, added new winglets, fly-by-wire
spoilers and big displays for the next generation of pilots. It
pushed technology, as it had done time and time again with
ever-increasing costs, to deliver a product that made its jets
more-efficient and less-costly to fly.

In the case of the 737 Max, with its nose pointed high in the air,
the larger engines — generating their own lift — nudged it even
higher. The risk Boeing found through analysis and later flight
testing was that under certain high-speed conditions both in
wind-up turns and wings-level flight, that upward nudge created a
greater risk of stalling. Its solution was MCAS, the
Maneuvering Characteristics Augmentation System control law that
would allow for both generations of 737 to behave the same way.
MCAS would automatically trim the horizontal stabilizer to bring
the nose down, activated with Angle of Attack data. It’s now at
the center of the Lion Air investigation and stalking the
periphery of the Ethiopian crash.